Pope Francis has been accused of encouraging illegal immigration after expressing solidarity with asylum seekers and economic refugees during a visit to the island of Lampedusa this week.

During his visit on Monday, Francis called for greater compassion for the tens of thousands of migrants from Africa and the Middle East who each year make the hazardous crossing from Tunisia and Libya to the remote island, Italy's southernmost territory.

He said the migrants were "brothers and sisters of ours trying to escape difficult situations to find some serenity and peace."

He prayed for the thousands of migrants who have drowned in the Mediterranean during boat sinkings – "they were looking for a better place for themselves and their families, but instead they found death," he said.

While his remarks, made at an open air Mass near the island's main harbour, were praised by humanitarian organisations, they were sharply criticised by members of Silvio Berlusconi's PDL party and by the anti-immigration Northern League.

"I'd be happy if one of the boats sank," said Erminio Boso, a hard-line member of the Northern League. "I don't give a toss for what the Pope said." Fabrizio Cicchitto, a senior member of Mr Berlusconi's People of Freedom party, said there was a danger that the Pope's remarks would encourage "dangerous and irregular" immigration run by criminal gangs of people traffickers.

The Pope should restrict himself to "preaching" and not get involved in immigration policies, the MP said.

He said Italy should not "let its guard down" against the influx of boat people from the North African coast.

Daniele Santanche, a staunch ally of Mr Berlusconi and an MP in his party, accused centre-Left politicians of using the Pope's remarks to whip up a row over the treatment of refugees.

"(They) manipulate the mission of faith and brotherhood of the Holy Father...Shame on them," she said.

Since the Pope's visit to Lampedusa on Monday, around 560 migrants reached the island, with the Right claiming that thousands more would be encouraged to make the journey because of Francis's compassionate stance.

"The Pope effect – the arrivals pick up," was the headline on Wednesday in Il Giornale, a conservative newspaper owned by Mr Berlusconi's brother.